Burn-off contact arrangement

ABSTRACT

A switching arrangement having a large burn-up reserve, contact fingers ( 2 ) are connected to a first electrical terminal via flexible bands ( 6 ) consisting of strips of, for example, copper which lie one above the other. The connecting portion ( 7 ) of the band ( 6 ), the said connecting portion adjoining the contact fingers ( 2 ) and being rigidly connected to them, is reinforced in each case by pressure welding of the strips. In the switch-off state, the bands ( 6 ) and, in part, the contact fingers ( 2 ) bear on an outwardly pointing supporting face ( 10 ), whilst, in the switch-on state, at least the contact fingers ( 2 ) and connecting portions ( 7 ) are lifted off from the supporting face ( 10 ), with the bands ( 6 ) being bent at the same time, as a result of contact with the outside of a switching pin ( 3 ) displaceable along a switching axis ( 1 ). The pressure force caused by electromagnetic attraction between the relatively short contact fingers ( 2 ) and the connecting portions ( 7 ), which in each case form an angle of approximately 30° with the switching axis ( 1 ), approximately compensates the contact lift-off forces, whilst the forces acting on the flexible parts of the bands ( 6 ) are absorbed essentially by the supporting face ( 10 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a burn-up switching arrangement, in particularfor circuit breakers, such as are used in power stations, transformerstations and other facilities for the supply of electrical energy forswitching on and off operating currents and overcurrents.

2. Description of the Related Art

Generic burn-up switching arrangements are known (see, for example,DE-A-196 13 568), in which the contact fingers of a contact bell areanchored fixedly, so that the pressure force in the switch-on positionis generated merely by the generally low elasticity of the contactfingers. In arrangements of this type, the burn-up reserve is restrictedto the initial elastic deflection of the contact fingers.

SUMMARY OF THE INVENTION

By contrast, the object on which the invention is based is to specify aburn-up switching arrangement which has a burn-up reserve not restrictedby the material properties of the contact fingers.

This object is achieved by means of a burn-up switching arrangement, inwhich the contact fingers have a large radial clearance available, sothat even a considerable burn-up can be compensated by a suitablevariation in the position of the contact fingers.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawing illustrates an exemplary embodiment which serves merely forexplaining the invention.

FIG. 1 shows diagrammatically an axial longitudinal section through aburn-up switching arrangement according to the invention, in theswitch-on position on the left and in the switch-off position on theright.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The burn-up switching arrangement illustrated in FIG. 1 has, as a firstswitching piece, a contact bell which is connected to a first electricalterminal and which is composed of a plurality of contact fingers 2 whichare arranged around a switching axis 1 and form an angle ofapproximately 30° with the latter and which consist completely or atleast in the region of the burn-up heads of material resistant toburn-up, such as, for example, W/Cu, graphite, CFC, graphite/Cu, CFC/Cu.Provided as a second switching piece is a solid switching pin 3 whichhas a tip 4 consisting likewise of material resistant to burn-up. Thesaid pin is connected to a second electrical terminal, for example via asliding bell or a flexible lead, and is displaceable along the switchingaxis 1, by means of a switching drive (not illustrated), between aswitch-on position, in which the contact fingers 2 touch the said pin onits outside, and a switch-off position, in which it is at a distancefrom these contact fingers.

In the continuation of each contact finger 2, the latter has adjoiningit a lead which is preferably welded to it and which connects itelectrically conductively to a housing part 5 and, further, to the firstelectrical terminal. The lead is formed in each case by a band 6 whichconsists of a plurality of strips of flexible electrically conductivematerial, for example of copper or a copper-containing alloy, which arelaid one above the other. In the region of connecting portions 7 whichdirectly adjoin the contact fingers 2 in the direction of the latter,the bands 6 are in each case reinforced by means of pressure-welding ofthe strips. Otherwise, however, the strips are not fixedly connected toone another, so that the band 6 is flexible in each case from the outerend of the connecting portion 7 onwards. A leaf spring 8 in each casepresses elastically from outside against the connecting portion 7, sothat the contact finger 2 is pressed against the switching pin 3 in theswitch-on position.

A supporting body 9 consisting of electrically insulating material formsan outwardly pointing supporting face 10 which is in the form of theenvelope of a cone frustum and on which, in the switch-off position, insmall part, the contact fingers 2 and, in a part extending considerablybeyond the connecting portion 7, the bands 6 bear with their insidesunder the action of the leaf springs 8. Moreover, the said supportingbody forms a central nozzle 11 which widens in the switch-on directionand into which the switching pin 3 projects in the switch-on position.

In the switch-on position illustrated on the left, the ends of thecontact fingers 2 are pressed against the outer face of the switchingpin 3 by the leaf springs 8. At least the contact fingers 2 and therigid connecting portions 7 adjoining them are lifted off from thesupporting face 10 as a,result of contact with the switching pin 3, but,as a rule, a part of the flexible region of the band 6 which adjoins theconnecting portion 7 is also thus lifted off. If, after the commencementof a switch-off, the current is commutated from a nominal-currentswitching arrangement, not illustrated, to the burn-up switchingarrangement, then, under the current intensities normally to beexpected, the lift-off forces between the switching pin 3 and thecontact fingers 2 are approximately compensated by the mutual attractionof the contact fingers 2 which is caused by the axial components of thepart-currents flowing through them.

Under very high currents, the flexible portions of the bands 6 arepressed completely against the supporting face 10, as illustrated on theleft in FIG. 1, so that the support body 9 absorbs the forces acting onthese. Consequently, in each case only those forces which act directlyon the relatively short, straight, obliquely set portion which is formedby the contact finger 2 and the connecting portion 7 rigidly continuingthe latter and is characterized by the axial length L and the radius Rare critical for the pressure exerted on the switching pin 3 by thecontact finger 2. This avoids the situation where the said pressureassumes undesirably high values leading to high abrasion and impedingthe switch-off movement.

As the switch-off movement continues, an arc 12 is thrown between theswitching pin 3 and the contact fingers 2 and is extinguished byblowing, thus causing a gas stream through the nozzle 11. The shorteningof the contact fingers 2 by burn-up is readily compensated in that theangle between the switching axis 1 and the rigid portion consisting ofthe contact finger 2 and connecting portion 7 in the switch-on positionis correspondingly increased. This adaptation of the position of thecontact fingers 2 is possible as long as the said portion does not bearon the supporting face 10, so that the burn-up reserve is very high, asmay be inferred immediately, above all, from the right-hand side of FIG.1.

Many modifications of the exemplary embodiment described are possiblewithin the scope of the invention. Thus, for example, the angle of thesupporting face and therefore also the upper limit of the angle of thecontact fingers with the switching axis may. be selected differently. Itis preferably between 15° and 45°, with the switching axis taken in theswitch-on direction. The switching pieces may also be supplemented byother components, for example, in each case, a burn-up ring may beprovided, which precedes the contact bell or, in the switch-offposition, the switching pin, or a burn-up ring of this type may also bearranged on only one side.

What is claimed is:
 1. A burn-up switching arrangement, with a firstswitching piece which, in a switch-on position, is connected to a firstelectrical terminal and which comprises a contact bell with a pluralityof contact fingers, and with a second switching piece which, in theswitch-on position, is connected to a second electrical terminal andwhich comprises a switching pin which can be moved relative to the firstswitching piece, along a switching axis, between the switch-on position,in which the contact fingers of the contact bell touch the switching pinon its outside, so that the burn-up switching arrangement closes acurrent path between the first terminal and the second terminal, and aswitch-off position, in which the switching pin is at a distance fromthe first switching piece, the contact fingers of the contact bell beingconnected to the first electrical terminal via a flexible lead whichallows a change in an angle between a longitudinal axis of the contactfingers and the switching axis, and at least one supporting face beingprovided for supporting at least part of the flexible lead, wherein theat least one supporting face is formed by a continuous outside of asupporting body, in that the supporting body includes electricallyinsulating material at least in the at least one supporting face, and inthat an inside of the supporting body is an insulating nozzle wideningin the switch-on direction, said supporting body being positioned so asto prevent inward elastic action of the contact fingers toward theswitching axis.
 2. The burn-up switching arrangement according to claim1, wherein the flexible lead includes a plurality of bands includingflexible electrically conductive material.
 3. The burn-up switchingarrangement according to claim 1, wherein each band directly adjoins acontact finger.
 4. The burn-up switching arrangement according to claim2, wherein each band includes a plurality of strips of the flexibleelectrically conductive material which are laid one above the other. 5.The burn-up switching arrangement according to claim 2, wherein theflexible electrically conductive material is copper or acopper-containing alloy.
 6. The burn-up switching arrangement accordingto claim 2, wherein the strips of a band are in each case connected toone another at a connecting portion adjoining the contact finger.
 7. Theburn-up switching arrangement according to claim 1, wherein the contactfingers are substantially straight and in each case form an angle withthe switching axis.
 8. The burn-up switching arrangement according toclaim 7, wherein the angle between a longitudinal axis of the contactfinger and the switching axis in the switch-on direction is in each casebetween 15° and 45°.
 9. The burn-up switching arrangement according toclaim 1, wherein the contact fingers uniformly surround the switchingaxis.
 10. The burn-up switching arrangement according to claim 1,wherein it has, for each contact finger, at least one pressure elementwhich, in the switch-on position, subjects the contact finger to apressure force directed towards the switching pin.
 11. The burn-upswitch arrangement according to claim 6, wherein the strips of a bandare in each case connected to one another by pressure welding.